Refrigeration system having adjustable refrigeration capacity

ABSTRACT

A subcooling heat exchanger and subcooling expansion valve in a refrigeration system provide subcooling of a pre-subcooled portion, for refrigerating a thermal load, of condensed refrigerant liquid by a pre-subcooling portion of the condensed refrigerant liquid. The amount of subcooling of the pre-subcooled portion is determined by measuring, with a pressure sensor, refrigerating suction pressure exerted by refrigerating compressors of the system. A controller then controls, based on the refrigerating suction pressure, modulation of mass of pre-subcooling portion, relative pre-subcooled portion, and expansion thereof in the subcooling expansion valve, which controls the amount of refrigerant heat exchanged, and therefore subcooling of pre-subcooled portion, between the pre-subcooling portion and the pre-subcooled portion in the subcooling heat exchanger. The pre-subcooling portion is then subsequently compressed by a subcooling compressor.

FIELD OF THE INVENTION

The present invention concerns refrigeration systems and methods, and more particularly a refrigeration system having adjustable refrigeration capacity, as well as means and methods for adjusting the refrigeration capacity thereof.

BACKGROUND OF THE INVENTION

Refrigeration systems are commonly used in supermarkets to refrigerate or to maintain in frozen state perishable products, such as foodstuff. Conventionally, refrigeration systems include multiple refrigerating compressors and evaporators. Refrigerating compressors compress a refrigerant, often received thereby from evaporators in the form of refrigerant vapor, into compressed refrigerant, i.e. compressed refrigerant vapors, thus increasing the pressure and temperature thereof. The high-pressure, high-temperature compressed refrigerant is then circulated to a condenser, such as an outdoor air-cooled condenser, a liquid-cooled indoor condenser or the like. The latent heat of the high-pressure compressed refrigerant is absorbed in the condenser by the ambient air or by liquid circulating therein. As a result, the compressed refrigerant is condensed into a condensed refrigerant, i.e. a condensed refrigerant liquid. The condensed refrigerant liquid is then fed through refrigerating expansion valves, thus reducing the pressure and temperature thereof, to the evaporators, where the refrigerant absorbs load heat from a thermal load, such as, for example, foodstuffs, proximal to the evaporators and refrigerated by the system. The absorption of load heat in the evaporator causes the refrigerant to evaporate into low pressure, low temperature refrigerant vapor which is then circulated from the evaporator to the compressors to recommence the refrigeration cycle.

Typically, the refrigeration capacity of refrigeration systems is selected for the maximum thermal load, i.e. the load of foodstuffs, etc. that must be refrigerated thereby. However, as the maximum thermal load will not always be present, adjustment, i.e. modulation, of the refrigeration capacity of the refrigeration system is required in order to maintain the balance between the thermal load and the supplied refrigeration capacity. Otherwise, the thermal load may be refrigerated too much or too little. For example, an excess refrigeration capacity could result in unwanted freezing of the thermal load. Conversely, insufficient refrigeration capacity could result in insufficient refrigeration of the thermal load, which could cause, for example when the thermal load includes foodstuffs, spoilage or degradation thereof.

To adjust refrigeration capacity, most conventional refrigeration systems simply stop and start, i.e. actuate and deactuate, one or more of the refrigerating compressors to increase or decrease refrigeration capacity. For example, stopping one of the refrigerating compressors reduces the level of compression of refrigerant vapors and/or the speed of flow of refrigerant through the system, thus reducing the refrigeration capacity. Conversely, starting an additional refrigerating compressor will increase the level of compression and/or the speed of flow of refrigerant through the refrigeration system and increase refrigeration capacity thereof. However, as the refrigeration capacity of any number of refrigerating compressors, when running, rarely corresponds exactly to the refrigeration capacity required, one or more refrigerating compressors must often be started and stopped very frequently to match the refrigeration capacity currently generated by the system to the refrigeration capacity exactly required for refrigerating the thermal load to a desired temperature. Unfortunately, such frequent stopping and starting of a compressor tends to reduce the lifespan thereof. Further, constant starting and stopping of one or more refrigerating compressors in short periods of time also causes the refrigeration suction pressure of system, i.e. the total pressure exerted by all refrigerating compressors that are actuated at any given time to draw refrigerant thereinto for compression, to fluctuate, with the fluctuation becoming more extreme as more compressors are started and stopped in a short period of time. Thus, as more refrigerating compressors are started and stopped in a given period of time and/or the length of time between starting and stopping a given number of refrigerating compressors is reduced, it becomes increasingly difficult to maintain the refrigeration suction pressure within an optimal range.

Accordingly, it would be desirable to have an improved refrigeration system in which refrigeration capacity may be adjusted with less frequent starting and stopping of refrigerating compressors.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved refrigeration system with adjustable refrigeration capacity.

An advantage of the present invention is that the refrigeration capacity of the refrigeration system may be adjusted gradually.

A further advantage of the present invention is that starting and stopping of refrigerating compressors is reduced when adjusting the refrigeration capacity of the refrigeration system.

In a first aspect, the present invention provides an adjustment system for adjusting refrigeration capacity of a refrigeration system having a plurality of refrigerating compressors in fluid communication with at least one refrigerant condensing means and at least one evaporator, the adjustment system comprising:

-   -   a subcooling heat exchanger in fluid communication with the         refrigerant condensing means and the evaporator and situated         therebetween, the subcooling heat exchanger receiving a         pre-subcooled portion and a pre-subcooling portion of a         condensed refrigerant liquid from the refrigerant condensing         means, the pre-subcooling portion subcooling the pre-subcooled         portion into a subcooled portion of the condensed refrigerant         liquid in the subcooling heat exchanger by absorbingly         exchanging refrigerant heat therewith, the pre-subcooling         portion being evaporated thereby into a subcooling portion of         refrigerant vapor, a subcooled refrigerating portion of the         subcooled portion circulating from the subcooling heat exchanger         to the evaporator for absorbing a load heat from a thermal load         situated proximal the evaporator and thereby refrigerating the         thermal load, the subcooled refrigerating portion being         evaporated by absorbing the load heat in the evaporator into a         corresponding refrigerating portion of refrigerant vapor;     -   a subcooling expansion valve in fluid communication with the         refrigerant condensing means and the subcooling heat exchanger         and disposed therebetween, the subcooling expansion valve         selectively modulating mass of the pre-subcooling portion,         relative the pre-subcooled portion, circulated therethrough into         the subcooling heat exchanger and expansion of the         pre-subcooling portion therein, the subcooling expansion valve         thereby selectively adjusting the refrigerant heat absorbed from         the pre-subcooled portion and thereby the load heat absorbable         by the subcooled refrigerating portion from the thermal load,         thereby adjusting the refrigerant capacity of the refrigeration         system; and     -   a subcooling compressor in fluid communication with the         subcooling heat exchanger and the refrigerant condensing means,         the subcooling compressor exerting a subcooling suction pressure         for drawing the pre-subcooled portion through the subcooling         expansion valve and the subcooling heat exchanger and receiving         the subcooling portion, the subcooling portion being compressed         thereby.

In a second aspect, the present invention provides a refrigeration system having an adjustable refrigeration capacity, the refrigeration system comprising:

-   -   a plurality of refrigerating compressors;     -   at least one refrigerant condensing means in fluid communication         with the refrigerating compressors for condensing a refrigerant         into a condensed refrigerant liquid;     -   at least one evaporator in fluid communication with the         refrigerant condensing means and the refrigerating compressors         and in which a subcooled refrigerating portion of the condensed         refrigerant liquid is evaporated into a refrigerated portion of         refrigerant vapor by absorption of a load heat from a thermal         load situated proximal the evaporator and refrigerated by the         refrigeration system, the refrigerating portion being circulated         from the evaporator to at least one of the refrigerating         compressors;     -   a subcooling heat exchanger in fluid communication with the         refrigerant condensing means and the evaporator and situated         therebetween, the subcooling heat exchanger receiving a         pre-subcooled portion and a pre-subcooling portion of the         condensed refrigerant liquid, the pre-subcooling portion         subcooling the pre-subcooled portion into a subcooled portion of         the condensed refrigerant liquid in the heat exchanger by         absorbingly exchanging refrigerant heat therewith, the         pre-subcooling portion being evaporated thereby into a         subcooling portion of refrigerant vapor, the subcooled         refrigerating portion being drawn from the subcooled portion and         circulated to the evaporator;     -   a subcooling expansion valve in fluid communication with the         refrigerant condensing means and the heat exchanger and disposed         therebetween, the subcooling expansion valve selectively         modulating mass of the pre-subcooling portion, relative the         pre-subcooled portion, circulated therethrough into the         subcooling heat exchanger and expansion of the pre-subcooling         portion therein, the subcooling expansion valve thereby         selectively adjusting the refrigerant heat absorbed from the         pre-subcooled portion and thereby the load heat absorbable by         the subcooled refrigerating portion from the thermal load,         thereby adjusting the refrigerant capacity of the refrigeration         system; and     -   a subcooling compressor in fluid communication with the         subcooling heat exchanger and the refrigerant condensing means,         the subcooling compressor exerting a subcooling suction pressure         for drawing the pre-subcooled portion through the subcooling         expansion valve and the subcooling heat exchanger and receiving         the subcooling portion, the subcooling portion being compressed         thereby.

In a third aspect, the present invention provides a method for adjusting refrigerant capacity of a refrigeration system having a plurality of refrigerating compressors in fluid communication with at least one evaporator and at least one refrigerant condensing means, at least one of the compressors compressing a refrigerating portion, as refrigerant vapor, into compressed refrigerant, the refrigerant condensing means condensing the compressed refrigerant into condensed refrigerant liquid of which a subcooled refrigerating portion is evaporated, into the refrigerating portion, in the evaporator by absorption of a load heat from a thermal load refrigerated by the refrigeration system and circulated therefrom to at least one of the refrigerating compressors, the method comprising the steps of:

-   -   expanding a pre-subcooling portion of the condensed refrigerant         liquid in a subcooling expansion valve in fluid communication         with the refrigerant condensing means;     -   subcooling a pre-subcooled portion of the condensed refrigerant         liquid into a subcooled portion thereof, the subcooled         refrigerating portion being drawn from the subcooled portion,         with the pre-subcooling portion after the expanding by         exchanging of heat therebetween in a subcooling heat exchanger         in fluid communication with the refrigerant condensing means,         the evaporator, and the subcooling expansion valve, thereby         adjusting a quantity of load heat absorbable by the         refrigerating portion and the refrigeration capacity of the         refrigeration system.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects and advantages of the present invention will become better understood with reference to the description, provided for purposes of illustration only, in association with the following figure, wherein:

FIG. 1 is a schematic diagram of a refrigeration system having an adjustment system for adjusting refrigeration capacity thereof, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic diagram of a refrigeration system, shown generally as 10, having an adjustment system, shown generally as 12, for adjusting refrigeration capacity thereof. Broadly speaking, the system 10 includes at least one, but preferably two or more, refrigerating compressors 14, adjustment system 12, an outdoor air-cooled condenser 16 as a refrigerant condensing means, at least one evaporator 18, a refrigerant liquid receiver 20, one or more refrigeration expansion valves 22, and optionally, heat reclaim means 24. System 10 also includes a plurality of conduits, also referred to as lines and manifolds, through which refrigerant is circulated in system 10 for refrigerating therewith a thermal load between refrigerating compressors 14, adjustment system 12, refrigerant condensing means 16, evaporator 18, refrigerant liquid receiver 20, refrigeration expansion valves 22, and heat reclaim means 24, all of which are connected in fluid communication for refrigerant by conduits. Thermal load is typically situated in proximity to evaporators 18.

Adjustment system 12 includes: subcooling heat exchanger 28 connected in fluid communication for refrigerant to refrigerant condensing means 16 and evaporator 18 and situated therebetween, subcooling expansion valve 30 connected in fluid communication for refrigerant to refrigerant condensing means 16 and subcooling heat exchanger 28 and situated therebetween, controller 32 connected to subcooling expansion valve 30, and sensor 34 connected to controller 32. Adjustment system further includes a subcooling compressor 36 connected thereto in fluid communication therewith and with refrigerant condensing means 16 for compressing refrigerant received, as a subcooling portion of refrigerant vapor, from subcooling heat exchanger 28 and compressing the subcooling portion into compressed refrigerant vapor. Optional heat reclaim means 24 reclaims, during a heat reclaim cycle, latent refrigerant heat rejected by system 10 from refrigerant for circulating the rejected heat to heat another medium, such as air for comfort heating of a building or water. Optional heat reclaim means 24 is described in detail in U.S. patent application Ser. No. 11/103,523 which is incorporated herein by reference.

In the embodiment shown, refrigerating compressors 14 are used for refrigeration of thermal load only, i.e. for refrigeration cycles. Further, not all refrigerating compressors 14 need be activated, i.e. engaged, in the refrigeration cycle at any given time. Subcooling compressor 36, along with subcooling heat exchanger 28, subcooling expansion valve 30, controller 32, and sensor 34, are used during the refrigeration cycle to adjust refrigeration capacity of system 10, either selectively increasing or decreasing the refrigeration capacity thereof, until an additional refrigerating compressor 14 must be activated or a currently activated refrigerating compressor must be deactivated to regulate refrigeration capacity of system 10 to that required to refrigerate the thermal load. Thus, for a given number of actuated refrigerating compressors 14, i.e. compressors currently engaged in refrigeration, additional refrigerating compressors 14 are only activated when an increase in refrigeration capacity of system 10 beyond the maximum increase in refrigeration capacity that can be provided by subcooling with adjustment system 12 is required. Similarly, for a given number of actuated refrigerating compressors 14, an actuated compressor 14 engaged in refrigeration is deactuated generally only when a decrease in refrigeration capacity of system 10 beyond the maximum downward adjustment thereof that can be provided by subcooling with adjustment system 12 is required, for the number of actuated refrigerating compressors 14. Typically, increases and decreases in requirements for refrigerant capacity are, respectively, the result of increases and decreases in mass and/or temperature of thermal load. Adjustment compressor 36 may also be used for defrosting a frosted evaporator 18 during a defrost cycle for the system and, when heat reclaim means 24 is present, a heat reclaim cycle in which rejected refrigerant heat is reclaimed by heat reclaim means 24. The functioning of system 10, and notably adjustment system 12, during refrigeration cycles, defrost cycles, and heat reclaim cycles are explained in detail below.

During refrigeration cycles, refrigerating compressors 14 receive a refrigerating portion, as low pressure refrigerant vapor, of refrigerant circulated in system 10 from evaporators 18 connected in fluid communication therewith by refrigeration inlet conduits 38, 40, and 42. Specifically, a subcooled refrigerating portion of a subcooled refrigerant liquid circulated in system 10 is evaporated into a corresponding refrigerating portion of refrigerant vapor in evaporators 18 by absorbing of load heat from the thermal load. This absorption of load heat cools thermal load and provides refrigeration thereof. The refrigerating portion is then circulated therefrom through refrigeration vapor conduits 38, including through respective evaporator pressure regulating valves 44 situated thereon, to refrigeration inlet manifold 40, to which all refrigeration inlet conduits 38, 42 are connected. Refrigerating portion is then drawn from refrigeration inlet manifold 40 through refrigeration inlet conduits 42 into compressors 14 at respective refrigeration suction inlets 45 thereof by a refrigeration suction pressure exerted therefrom by refrigerating compressors 14 in conduits 38, 40, 42, which may also be referred to as refrigeration suction conduits. Within refrigerating compressor 14, refrigerating portion is subsequently compressed into a corresponding refrigerating compressor output portion of compressed refrigerant vapor having high temperature and pressure relative to refrigerating portion. At least a portion of refrigerating compressor output portion, referred to as a refrigerating compressor condensing portion, is circulated from refrigerating compressors 14 to refrigerant condensing means 16 through, in sequence, refrigerating compressor discharge conduits 46, 48 and condensing inlet conduit 50 which together connect refrigerating compressors 14 to refrigerant condensing means 16 in fluid communication therewith.

Refrigerant, including refrigerating compressor condenser portion, received in refrigerant condensing means 16 is condensed and cooled into condensed refrigerant liquid which is output from refrigerant condensing means to adjustment system 12, specifically subcooling heat exchanger 28 thereof, through first subcooling inlet conduit 54 and second subcooling inlet conduit 56 which connect refrigerant condensing means 16 to subcooling heat exchanger 28 in fluid communication therewith. Refrigerant condensing means 16 is connected directly to subcooling heat exchanger 28, namely to first subcooling exchanger inlet 55 by first subcooling inlet conduit 54.

A pre-subcooled portion of condensed refrigerant liquid, which is subcooled in subcooling heat exchanger, is received at first subcooling exchanger inlet 55 directly from first subcooling inlet conduit 54. Second subcooling inlet conduit 56 is connected to first subcooling inlet conduit 54 and extends therefrom through subcooling expansion valve 30, situated thereon between refrigerant condensing means 16 and subcooling heat exchanger 28 and connected thereby in fluid communication therewith. A second, pre-subcooling portion of condensed liquid refrigerant output from refrigerant condensing means 16, may, based on refrigeration capacity requirements determined by thermal load, be selectively and adjustably drawn, via subcooling expansion valve 30, from first subcooling inlet conduit 54 through second subcooling conduit 56 and subcooling expansion valve 30 before entering subcooling heat exchanger 28 in second subcooling heat exchanger inlet 57. Accordingly, subcooling expansion valve 30 modulates the quantity, i.e. mass, of pre-subcooling portion, and thereby flow of condensed refrigerant liquid therethrough. Subcooling suction pressure for drawing subcooling portion through second subcooling inlet conduit 56, subcooling expansion valve 30, and subcooling heat exchanger 28, is provided by subcooling compressor 36 connected to subcooling heat exchanger 28. Thus, condensed refrigerant liquid is divided into pre-subcooling portion and pre-subcooled portion, the pre-subcooling portion being the portion drawn through subcooling expansion valve 30 and second subcooling inlet conduit 56 and the pre-subcooled portion being the remaining portion, not drawn at any given moment through subcooling expansion valve 30. From heat exchanger 28, pre-subcooled portion is output, as a subcooled portion of the condensed refrigerant liquid, through subcooling outlet conduit 60. From conduit 60, a subcooled refrigerating portion of the subcooled portion is circulated to evaporators 18 via, in sequential order, evaporator inlet conduits 62, 64, drawn therethrough by refrigeration suction pressure exerted by refrigerating compressors 14. In evaporators 18, subcooled refrigerating portion absorbs load heat from thermal load, thus refrigerating thermal load, and is thereby evaporated into refrigerating portion of low-pressure refrigerant vapor, which is then circulated to refrigerating compressors for the next refrigeration cycle.

When pre-subcooling portion of condensed refrigerant liquid is drawn through subcooling expansion valve 30, it is expanded, thus lowering the temperature of the pre-subcooling portion to a subcooling temperature lower than the condensed temperature of condensed refrigerant liquid, notably pre-subcooled portion thereof, output from refrigerant condensing means 16 prior to passage through subcooling expansion valve 30. After passage through subcooling expansion valve 30, pre-subcooling portion of refrigerant passes through second subcooling inlet conduit 56 to subcooling heat exchanger 28 where it is exchanges refrigerant heat with first portion of refrigerant. As pre-subcooling portion, when entering subcooling heat exchanger 28, is at subcooling temperature, which is lower than condensed temperature and condensed pressure of pre-subcooled portion of refrigerant when pre-subcooled portion enters subcooling heat exchanger 28, pre-subcooling portion of refrigerant absorbs a subcooling quantity of refrigerant heat from subcooled portion of refrigerant while exchanging refrigerant heat therewith in subcooling heat exchanger 28, thus subcooling pre-subcooled portion into subcooled portion of refrigerant liquid having a subcooled temperature lower than condensed temperature. This lower subcooled temperature permits subcooled portion, and notably subcooled refrigerating portion thereof, to absorb additional load heat from thermal load, relative to what would otherwise be possible with pre-subcooled portion, thus increasing refrigeration capacity of system 10 without actuating an additional refrigerating compressor 14.

Circulation of second, subcooling portion of refrigerant, as well as modulation of the quantity, i.e. mass, of refrigerant liquid, is effected by subcooling expansion valve 30, in conjunction with controller 32 and sensor 34. Sensor 34 is connected to refrigerant inlet manifold 40 and constantly measures a refrigeration suction pressure exerted by refrigerating compressors 14 in manifold 40 and/or conduits 38, 42. This measurement of refrigeration suction pressure is transmitted, electronically or otherwise, over sensor connecting line to controller 32. Generally speaking, as thermal load increases and decreases, the demand for refrigeration capacity in system 10 increases and decreases therewith, i.e. the refrigeration capacity must increase and decrease with thermal load. The rate of circulation of refrigerant through system 10, generally speaking, increases and decreases as refrigeration capacity of system 10, respectively, increases and decreases. It is refrigerating compressors 14 which generally provide, by compression of refrigerant, circulation of the refrigerant through system 10 to evaporators 18. Accordingly, as thermal load and, thereby demand for refrigeration capacity, increases and decreases, refrigerating compressors 14 compress, respectively more or less refrigerant in a given period of time to, respectively, increase and decrease circulation of refrigerant through system to evaporators 18. Typically, increases and decreases in the amount, i.e. mass, of refrigerant circulated through system to evaporators is accomplished by, respectively, actuation of additional refrigerating compressors 14 to compress more refrigerant in a given period of time or deactivating refrigerating compressors 14 to reduce the amount of refrigerant compressed thereby in the same given period of time. Thus, as refrigerating compressors 14 increase and decrease rate of circulation of refrigerant to evaporators, demand for refrigerant vapor, i.e. refrigerating portion, by compressors 14 from evaporators 18 increases and decreases in tandem therewith, which, in turn, increases and decreases refrigeration suction pressure exerted by refrigerating compressors 14 in refrigeration inlet manifold 40 and/or conduits 38, 42. Accordingly, refrigeration suction pressure in refrigeration inlet manifold 40 and/or conduits 38, 42 is an expression of the demand for refrigeration capacity in system 10 based on thermal load refrigerated thereby.

Based on the measurement of the refrigeration suction pressure received by controller 32 from sensor 34, controller 32 selectively controls subcooling expansion valve 30 which draws condensed refrigerant liquid from first subcooling inlet conduit 54 therethrough via second subcooling conduit 56. More specifically, controller 32 adjusts subcooling expansion valve 30 to respectively increase or decrease the amount of liquid refrigerant, as pre-subcooling portion, circulated through subcooling expansion valve 30 in second subcooling inlet conduit 56 in response to increases and decreases in refrigeration suction pressure in refrigeration inlet manifold 40 to respectively increase and decrease subcooling of pre-subcooled portion of refrigerant liquid, and therefor the subcooled temperature of subcooled portion to respectively increase or decrease refrigeration capacity for a given number of actuated refrigerating compressors. Thus, refrigeration capacity for a given number of actuated refrigerating compressors 14 can be gradually increased and decreased by an amount equal to the maximum subcooling capacity of subcooling made available by subcooling heat exchanger 28 and subcooling expansion valve 30. This maximum subcooling capacity is represented by the amount of refrigerant liquid that can be circulated as pre-subcooling portion through subcooling expansion valve 30 and subcooling heat exchanger 28 at any given moment, as provided by subcooling expansion valve, before it becomes necessary to actuate or deactuate another refrigerating compressor 14. Alternatively, subcooling can be adjusted by increasing or decreasing the amount of expansion of pre-subcooling portion in subcooling expansion valve 28. If no subcooling is required at a given moment, then all of the condensed refrigerant liquid output from refrigerant condensing means 16 is circulated through subcooling heat exchanger 28 as pre-subcooled portion and no subcooling is effected.

As explained above, once subcooling of pre-subcooled portion into subcooled portion is effected in subcooling heat exchanger 28, subcooled portion exits subcooling heat exchanger through subcooling outlet conduit 60. From conduit 60, subcooled portion, and more specifically subcooled refrigerating portion thereof, may circulate directly through conduit 60 to evaporators 18 for refrigerating thermal load. Further, a subcooled desuperheating portion of subcooled portion may, as required, be circulated to subcooling compressor 36 for, as explained below, cooling refrigerant vapor received by subcooling compressor 36 from refrigerating compressors 14. To the extent that either the subcooled temperature of subcooled refrigerating portion or the quantity thereof that is available for evaporators 18 at any given moment can absorb additional load heat from thermal load in evaporator 18 than would otherwise be possible without subcooling, the refrigeration capacity of system 10 may be increased without actuating additional refrigerating compressors 14. Further, as refrigeration suction pressure in refrigeration inlet conduits 42 is constantly measured by sensor 34 and the amount of expansion of pre-subcooled portion in subcooling expansion valve and/or the amount of condensed refrigerant liquid circulated therethrough as pre-subcooled portion is constantly adjusted by controller 32 based on refrigeration suction pressure, the amount of subcooling provided by system 10 can be constantly and gradually adjusted. Should the thermal load be reduced, the demand for refrigeration capacity will also drop, causing a drop in refrigeration suction pressure in conduit 42. Accordingly, subcooling expansion valve 30 can also be adjusted to reduce the amount, i.e. mass, of pre-subcooling portion expanded therein or the amount of expansion thereof, thus gradually reducing the refrigerant capacity of system 10 without deactuating refrigerating compressors 14 that are currently actuated. It is only when the increase or decrease in refrigeration capacity required is greater than the adjustment possible by reducing or increasing the subcooling portion of condensed refrigerant liquid circulated through subcooling expansion valve 30 and/or the amount of expansion rendered by subcooling expansion valve 30 that a refrigerating compressor 14 will have to be actuated or deactuated.

With regard to pre-subcooling portion, pre-subcooling portion is evaporated into a subcooling portion of low pressure refrigerant vapor during expansion in subcooling expansion valve 28 and through absorption of refrigerant heat from pre-subcooled portion in subcooling heat exchanger 30. Subcooling portion exits from subcooling heat exchanger through subcooling compressor inlet conduit 80 which connects subcooling heat exchanger 28 in fluid communication with subcooling compressor 36.

From subcooling compressor inlet conduit 80, subcooling portion is drawn into subcooling compressor 36 by subcooling suction pressure exerted thereby. Subcooling portion is then compressed in subcooling compressor 36 into a subcooling compressor output portion of compressed refrigerant vapor at high temperature and high pressure relative subcooling portion. When required, as explained below, a bypass portion of refrigerating compressor output portion and subcooled desuperheating portion may also be received by subcooling compressor 36 and compressed thereby as part of subcooling compressor output portion. Subcooling portion is then circulated, as compressed refrigerant vapor, from subcooling compressor 36 through subcooling compressor discharge outlet conduit 82 and oil separator 84 disposed thereon. From subcooling discharge outlet conduit, subcooling compressor output portion is, generally speaking, circulated to refrigerant condensing means 16 and is condensed thereby into, along with at least a portion of refrigerating outlet portion, into condensed refrigerant liquid used for the refrigeration cycle. However, should defrosting of an evaporator 18 or heat reclaim be required, subcooling compressor output portion is, instead, respectively circulated to the evaporator 18 requiring defrosting, referred to as a frosted evaporator 18, or to heat reclaim means 24.

During a defrost cycle to defrost a frosted evaporator 18, subcooling compressor pressure regulating valve 88 disposed on conduit 82 closes at least partially, causing subcooling compressor output portion, to circulate through defrost inlet conduit 90, connected to subcooling compressor discharge outlet conduit 82 connecting subcooling compressor pressure regulating valve 88 and oil separator 84. At the same time, defrost control valve 86 on defrost inlet conduit 90 opens allowing the subcooling compressor output portion to circulate to evaporator defrost manifold conduit 92. From evaporator defrost manifold conduit 92, subcooling compressor output portion flows through evaporator defrost inlet conduit 94 connected thereto into conduit 38 and into evaporator 18, where refrigerant heat from subcooling compressor output portion is absorbed therefrom by frost in frosted evaporator 18, thus melting frost and defrosting evaporator 18. As refrigerant heat is absorbed from subcooling compressor output portion in evaporator 18, subcooling compressor output portion is at least partially condensed and exits evaporator 18 through evaporator inlet conduit 62. From evaporator inlet conduit 62, subcooling compressor output portion then circulates through defrost outlet conduit 98 back to refrigerant condensing means 16, where it is condensed, along with refrigerant vapor from compressors 14, 36 into condensed refrigerant liquid and forwarded through first subcooling inlet conduit 54 to subcooling heat exchanger 28.

Should a heat reclaim cycle be engaged to effect heat reclaim, subcooling defrost control valve 86 is closed and subcooling compressor pressure regulating valve 88 is opened, thus allowing subcooling compressor output portion to flow through conduit 82 to three-way motorized valve 100, connected to conduits 82, 102, 104 and disposed at the intersection thereof. Three-way motorized valve 100 directs the subcooling compressor output portion through heat reclaim inlet conduit 104 into heat reclaim means 24. In heat reclaim means 24, unused, i.e. rejected, refrigerant heat is absorbed from refrigerant vapor of subcooling compressor output portion by heat reclaim coils, thus at least partially condensing the subcooling compressor output portion. Subcooling compressor output portion exits heat reclaim means 24 through heat reclaim outlet conduit 106, which connects heat reclaim means 24 to refrigerant condensing means 16 in fluid communication therewith. In refrigerant condensing means 16, subcooling compressor output portion is condensed into refrigerant liquid. If heat reclaim and defrost are not required, defrost control valve 86 is closed and subcooling pressure regulating valve 88 is opened, and subcooling compressor output portion from subcooling compressor flows through conduit 82 to three-way motorized valve 100. However, when heat reclaim is not required, three-way motorized valve 100 directs circulation of subcooling compressor output portion refrigerant through conduit 102, connecting three-way motorized valve 100 and refrigerant condensing means 16, into refrigerant condensing means 16 where it is condensed into refrigerant liquid along with refrigerant vapor output from refrigerating compressors 14. Thus, subcooling compressor 36 is connected, in fluid communication, with refrigerant condensing means 16, by conduits 82, 102 and valves 88, 100 for refrigeration cycles. Subcooling compressor 36 is connected, in fluid communication, with refrigerant condensing means 24, by conduits 82, 104, 106 and valves 88, 100 for heat reclaim cycles.

To ensure that the supply of refrigerant vapor to subcooling compressor 36 is adequate to meet demand for subcooling, defrost, and heat reclaim at all times, a bypass portion of hot, high pressure refrigerant vapor from refrigerating compressor output potion, output by refrigerating compressors 14, is directed to subcooling compressor inlet conduit 80. Bypass passageway conduit 108 connects refrigeration discharge outlet conduit 50 to subcooling compressor inlet conduit 80. A bypass, pressure regulating valve 110, is connected to conduits 80, 108 and is disposed therebetween. Thus, subcooling compressor 36 is connected to refrigerating compressors 14. When additional refrigerant, in addition to subcooling portion, is required by subcooling compressor 36, bypass pressure regulating valve 110 opens, thus allowing subcooling compressor 36 to draw a bypass portion of refrigerating compressor output portion, already compressed to high temperature and pressure by refrigerating compressors 14, from conduit 50 through subcooling compressor inlet conduit 80 into subcooling compressor 36. Thus, subcooling compressor 36 is always provided with an adequate supply of refrigerant, which ensures that subcooling suction pressure exerted by subcooling compressor 36 in conduit 80 is essentially stable.

When bypass pressure regulating valve 110 opens to allow circulation of bypass portion from refrigerating compressor 14 through conduits 50, 108, 80 to subcooling compressor 36, a desuperheating expansion valve 114 is actuated on desuperheating conduit 112, which connects subcooling compressor inlet conduit 80 and subcooling outlet conduit 60. Thus, a subcooled desuperheating portion of subcooled refrigerant liquid is drawn through desuperheating conduit 112 and expanded in desuperheating expansion valve 114. The desuperheating portion, once expanded in desuperheating expansion valve 114, then circulates therefrom into subcooling compressor inlet conduit 80, where it mixes with high-temperature, high-pressure refrigerant vapor received from refrigerating compressors 14, thus maintaining a safe and stable suction temperature in conduit 80 and subcooling compressor 36.

Conduits 106, 54, 56, 102, 50, 48, 46, 108, 112, 54, 56, 60, 62, 64, 96, 98 92, 40, 38, 42, 80, 90, 82, 104, 94 may be made of any material known in the art that is suitable for circulation of refrigerant therein. Similarly, compressors 14, 36 may be any type of compressor typically used for a refrigeration system. Oil separators 84, evaporators 18, heat reclaim means 24, and refrigerant condensing means 16 may also be of any type that is typically used for refrigeration. Subcooling heat exchanger 28 is preferably a plate heat exchanger, although other types of heat exchangers, such as coil-based heat exchangers or the like, may be substituted therefore. Subcooling expansion valve is preferably an electronic step expansion valve, but any expansion valve capable of selectively and adjustably regulating, i.e. modulating, circulation of refrigerant therethrough and expansion thereof, under the control of controller 32, may be deployed. Controller 32 is preferably a proportional integral derivative (PID) controller. However, other controllers may be deployed provided they can receive measurements of refrigerating suction pressure from sensor 34 and selectively, adjustably, and gradually control the amount of condensed refrigerant liquid circulated through subcooling expansion valve 30 and the amount of expansion thereof, based on the measurements taken by sensor 34. Sensor connector line may be a conduit of any sort, electrical, fluid, or otherwise, capable of transmitting measurements from sensor 34 to controller 32.

It will be apparent to one skilled in the art that other embodiments of the present invention may be envisaged. The description provided herein is provided for purposes of illustration and not limitation. While a specific embodiment has been described, those skilled in the art will recognize many alterations that could be made within the spirit of the invention, which is defined solely according to the following claims. 

1. An adjustment system for adjusting refrigeration capacity of a refrigeration system having a plurality of refrigerating compressors in fluid communication with at least one refrigerant condensing means and at least one evaporator, said adjustment system comprising: a subcooling heat exchanger in fluid communication with the refrigerant condensing means and the evaporator and situated therebetween, said subcooling heat exchanger receiving a pre-subcooled portion and a pre-subcooling portion of a condensed refrigerant liquid from said refrigerant condensing means, said pre-subcooling portion subcooling said pre-subcooled portion into a subcooled portion of said condensed refrigerant liquid in said subcooling heat exchanger by absorbingly exchanging refrigerant heat therewith, said pre-subcooling portion being evaporated thereby into a subcooling portion of refrigerant vapor, a subcooled refrigerating portion of said subcooled portion circulating from said subcooling heat exchanger to said evaporator for absorbing a load heat from a thermal load situated proximal the evaporator and thereby refrigerating said thermal load, said subcooled refrigerating portion being evaporated by absorbing said load heat in the evaporator into a corresponding refrigerating portion of refrigerant vapor; a subcooling expansion valve in fluid communication with the refrigerant condensing means and said subcooling heat exchanger and disposed therebetween, said subcooling expansion valve selectively modulating mass of said pre-subcooling portion, relative said pre-subcooled portion, circulated therethrough into said subcooling heat exchanger and expansion of said pre-subcooling portion therein, said subcooling expansion valve thereby selectively adjusting said refrigerant heat absorbed from said pre-subcooled portion and thereby said load heat absorbable by said subcooled refrigerating portion from said thermal load, thereby adjusting the refrigerant capacity of the refrigeration system; and a subcooling compressor in fluid communication with said subcooling heat exchanger and the refrigerant condensing means, said subcooling compressor exerting a subcooling suction pressure for drawing said pre-subcooled portion through said subcooling expansion valve and said subcooling heat exchanger and receiving said subcooling portion, said subcooling portion being compressed thereby.
 2. The adjustment system of claim 1, wherein said subcooling heat exchanger is a plate heat exchanger.
 3. The adjustment system of claim 1, further comprising a controller connected to a sensor and to said subcooling expansion valve, said sensor taking a measure of the thermal load and said controller controlling, based on said measure, modulation of said mass of said pre-subcooled portion and of said expansion thereof in said subcooling expansion valve.
 4. The adjustment system of claim 1, wherein said subcooling expansion valve is an electronic step expansion valve.
 5. The adjustment system of claim 3, wherein said controller is a proportional integral derivative controller.
 6. The adjustment system of claim 3, wherein the evaporator and the refrigerating compressors are connected in fluid communication by at least one refrigeration suction conduit and said sensor is a pressure sensor connected to said refrigeration suction conduit for sensing, as said measure, a refrigeration suction pressure exerted therewithin by the refrigerating compressor for drawing the refrigerating portion theretowards from said evaporator, said refrigeration suction pressure generally increasing and decreasing as said thermal load, respectively, increases and decreases.
 7. The adjustment system of claim 1, further comprising a bypass pressure regulating valve in fluid communication with said subcooling compressor and the refrigerating compressors and situated therebetween, said bypass pressure regulating valve opening and closing to respectively enable and disable circulation of compressed refrigerant vapor compressed by the refrigerating compressors to said subcooling compressor for compression thereby, along with said subcooling portion.
 8. The adjustment system of claim 7, further comprising a desuperheating expansion valve in fluid communication with said subcooling compressor and said subcooling heat exchanger and situated therebetween, said desuperheating expansion valve enabling a subcooled desuperheating portion of said subcooled portion to circulate therethrough into said subcooling compressor and expanding said subcooled desuperheating portion, thereby cooling said subcooling portion and said compressed refrigerant received by said subcooling compressor through said bypass pressure regulating valve.
 9. A refrigeration system having an adjustable refrigeration capacity, said refrigeration system comprising: a plurality of refrigerating compressors; at least one refrigerant condensing means in fluid communication with said refrigerating compressors for condensing a refrigerant into a condensed refrigerant liquid; at least one evaporator in fluid communication with said refrigerant condensing means and said refrigerating compressors and in which a subcooled refrigerating portion of said condensed refrigerant liquid is evaporated into a refrigerated portion of refrigerant vapor by absorption of a load heat from a thermal load situated proximal said evaporator and refrigerated by said refrigeration system, said refrigerating portion being circulated from said evaporator to at least one of said refrigerating compressors; a subcooling heat exchanger in fluid communication with the refrigerant condensing means and said evaporator and situated therebetween, said subcooling heat exchanger receiving a pre-subcooled portion and a pre-subcooling portion of said condensed refrigerant liquid, said pre-subcooling portion subcooling said pre-subcooled portion into a subcooled portion of said condensed refrigerant liquid in said heat exchanger by absorbingly exchanging refrigerant heat therewith, said pre-subcooling portion being evaporated thereby into a subcooling portion of refrigerant vapor, said subcooled refrigerating portion being drawn from said subcooled portion and circulated to said evaporator; a subcooling expansion valve in fluid communication with said refrigerant condensing means and said heat exchanger and disposed therebetween, said subcooling expansion valve selectively modulating mass of said pre-subcooling portion, relative said pre-subcooled portion, circulated therethrough into said subcooling heat exchanger and expansion of said pre-subcooling portion therein, said subcooling expansion valve thereby selectively adjusting said refrigerant heat absorbed from said pre-subcooled portion and thereby said load heat absorbable by said subcooled refrigerating portion from said thermal load, thereby adjusting the refrigerant capacity of said refrigeration system; and a subcooling compressor in fluid communication with said subcooling heat exchanger and said refrigerant condensing means, said subcooling compressor exerting a subcooling suction pressure for drawing said pre-subcooled portion through said subcooling expansion valve and said subcooling heat exchanger and receiving said subcooling portion, said subcooling portion being compressed thereby.
 10. The refrigeration system of claim 9, wherein said subcooling heat exchanger is a plate heat exchanger.
 11. The refrigeration system of claim 9, further comprising a controller connected to a sensor and to said subcooling expansion valve, said sensor taking a measure of the thermal load and said controller controlling, based on said measure, modulation of said mass of said pre-subcooled portion and of said expansion thereof in said subcooling expansion valve.
 12. The refrigeration system of claim 9, wherein said subcooling expansion valve is an electronic step expansion valve.
 13. The refrigeration system of claim 11, wherein said controller is a proportional integral derivative controller.
 14. The refrigeration system of claim 11, wherein said evaporator and said refrigerating compressors are connected in fluid communication by at least one refrigeration suction conduit and said sensor is a pressure sensor connected to said refrigeration suction conduit for sensing, as said measure, a refrigeration suction pressure exerted therewithin by the refrigerating compressor for drawing the refrigerating portion theretowards from said evaporator, said refrigeration suction pressure generally increasing and decreasing as said thermal load, respectively, increases and decreases.
 15. The refrigeration system of claim 9, further comprising a bypass pressure regulating valve in fluid communication with said subcooling compressor and said refrigerating compressors and situated therebetween, said bypass pressure regulating valve opening and closing to respectively enable and disable circulation of compressed refrigerant vapor compressed by said refrigerating compressors to said subcooling compressor for compression thereby, along with said subcooling portion.
 16. The refrigeration system of claim 15, further comprising a desuperheating expansion valve in fluid communication with said subcooling compressor and said subcooling heat exchanger and situated therebetween, said desuperheating expansion valve enabling a subcooled desuperheating portion of said subcooled portion to circulate therethrough into said subcooling compressor and expanding said subcooled desuperheating portion, thereby cooling said subcooling portion and said compressed refrigerant received by said subcooling compressor through said bypass pressure regulating valve.
 17. The refrigeration system of claim 16, wherein said subcooling compressor is connected to said evaporator by a defrost conduit through which a subcooling compressor output portion of said refrigerant, said subcooling compressor output portion being compressed refrigerant vapor compressed by said subcooling compressor, is circulated into said evaporator when said evaporator is frosted, said subcooling compressor output portion melting frost situated within said evaporator and thereby defrosting said evaporator.
 18. The refrigeration system of claim 16, further comprising a heat reclaim means connected in fluid communication by at least one conduit to said subcooling compressor and to the refrigerant condensing means, a subcooling compressor output portion of said refrigerant, said subcooling compressor output portion being compressed refrigerant vapor compressed by said subcooling compressor, being circulated, during a heat reclaim cycle, through said at least one conduit from said subcooling compressor through said heat reclaim means to said refrigerant condensing means, said heat reclaim means absorbing, and thereby reclaiming, a rejected refrigerant heat from said subcooling compressor output portion.
 19. A method for adjusting refrigerant capacity of a refrigeration system having a plurality of refrigerating compressors in fluid communication with at least one evaporator and at least one refrigerant condensing means, at least one of the compressors compressing a refrigerating portion, as refrigerant vapor, into compressed refrigerant, the refrigerant condensing means condensing the compressed refrigerant into condensed refrigerant liquid of which a subcooled refrigerating portion is evaporated, into said refrigerating portion, in the evaporator by absorption of a load heat from a thermal load refrigerated by said refrigeration system and circulated therefrom to at least one of the refrigerating compressors, said method comprising the steps of: expanding a pre-subcooling portion of the condensed refrigerant liquid in a subcooling expansion valve in fluid communication with the refrigerant condensing means; subcooling a pre-subcooled portion of said condensed refrigerant liquid into a subcooled portion thereof, said subcooled refrigerating portion being drawn from said subcooled portion, with said pre-subcooling portion after said expanding by exchanging of heat therebetween in a subcooling heat exchanger in fluid communication with said refrigerant condensing means, said evaporator, and said subcooling expansion valve, thereby adjusting a quantity of load heat absorbable by said refrigerating portion and the refrigeration capacity of said refrigeration system.
 20. The method of claim 19, further comprising the steps of: prior to said expanding, measuring a refrigeration suction pressure exerted by said refrigerating compressors for refrigerating said thermal load with a sensor connected to a controller for controlling said subcooling expansion valve; and based on said measuring, modulating, with said controller, mass of said pre-subcooling portion, relative said pre-subcooled portion, circulated through said subcooling expansion valve and said expanding of said pre-subcooling portion therein. 